The present embodiment relates generally to a method and cement composition for sealing a subterranean zone penetrated by a well bore.
In the drilling and completion of an oil or gas well, a cement composition is often introduced in the well bore for cementing pipe string or casing. In this process, known as “primary cementing,” the cement composition is pumped into the annular space between the walls of the well bore and the casing. The cement composition sets in the annular space, supporting and positioning the casing, and forming a substantially impermeable barrier, or cement sheath, which isolates the well bore from subterranean zones.
Changes in pressure or temperature in the well bore over the life of the well can produce stress on the cement composition. Also, activities undertaken in the well bore, such as pressure testing, well completion operations, hydraulic fracturing, and hydrocarbon production can impose stress. When the imposed stresses exceed the stress at which the cement fails, the cement sheath can no longer provide the above-described zonal isolation. Compromised zonal isolation is undesirable, and necessitates remedial operations to be undertaken.
Due to its incompressible nature, neat cement is undesirable for use where there is a chance of expansion or contraction in the well bore. In the past, components such as fumed silica have been added to lower the Young's modulus of cement compositions. However, fumed silica is often subject to shortages, and hence to undesirable variations in costs.
Therefore, a cement composition that can provide elasticity and compressibility, while retaining high compressive and tensile strengths, is desirable.